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+---
+title: Testing npm ci reproducible dependencies
+date: 2018-08-01
+---
+When [[https://blog.npmjs.org/post/161081169345/v500][npm@5]] came and along bringing [[https://docs.npmjs.com/files/package-locks][package-locks]] with it, I was confused on the benefits it provided, since running =npm install= more than once could resolve all the dependencies again and yield yet another =package-lock.json= fresh file. The message saying "you should add this file to version control" left me hesitant on what to do[fn:npm-install].
+
+However the [[https://blog.npmjs.org/post/171556855892/introducing-npm-ci-for-faster-more-reliable][addition of =npm ci= ]] filled this gapped: it's a more strict variation of =npm install= which guarantees that "[[https://docs.npmjs.com/files/package-lock.json][subsequent installs are able to generate identical trees]]". But are they really identical? I could see that I didn't have the same problems of different installation outputs, but I didn't know for sure if it was really identical.
+** Computing the hash of a directory's content
+I quickly searched for a way to check for the hash signature of a full combined directory tree, but I couldn't find one. I've made a poor man's [[https://en.wikipedia.org/wiki/Merkle_tree][Merkle tree]] implementation using =sha256sum= and a few piped comands at the terminal:
+#+BEGIN_SRC bash -n
+  merkle-tree () {
+    dirname="${1-.}"
+    pushd "$dirname"
+    find . -type f              | \
+      sort                      | \
+      xargs -I{} sha256sum "{}" | \
+      sha256sum                 | \
+      awk '{print $1}'
+    popd
+  }
+#+END_SRC
+Going through it line by line:
+- at #1 we create a Bash function called =merkle-tree=;
+- at #2 it accepts a single argument: the directory to compute the merkle tree from. If nothing is given, it runs on the current directory (=.=);
+- at #3 we go to the directory, so we don't get different prefixes in =find='s output (like =../a/b=);
+- at #4 we get all files from the directory tree. Since we're using =sha256sum= to compute the hash of the file contents, we need to filter out folders from it;
+- at #5 we need to sort the output, since different filesystems and =find= implementations may return files in different orders;
+- at #6 we use =xargs= to compute the hash of each file individually through =sha256sum=. Since a file may contain spaces we need to embed it within quotes;
+- at #7 we compute the hash of the combined hashes. Since =sha256sum= output is formatted like =<hash> <filename>=, it produces a different final hash if a file ever changes name without changing it's content;
+- at #8 we get the final hash output, excluding the =<filename>= (which is =-= in this case, aka =stdin=).
+
+Positive points:
+
+1. ignore timestamp: running more than once on different installation yields the same hash;
+
+Limitations:
+
+1. it ignores empty folders from the hash computation;
+2. the implementation's only goal is to represent using a digest whether the content of a given directory is the same or not. Leaf presence checking is obviously missing from it.
+
+Testing locally with sample data:
+#+BEGIN_SRC bash -n
+  mkdir /tmp/merkle-tree-test/
+  cd /tmp/merkle-tree-test/
+  mkdir -p a/b/ a/c/ d/
+  echo "one"   > a/b/one.txt
+  echo "two"   > a/c/two.txt
+  echo "three" > d/three.txt
+  merkle-tree . # output is       be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3
+  merkle-tree . # output still is be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3
+  echo "four"  > d/four.txt
+  merkle-tree . # output is now   b5464b958969ed81815641ace96b33f7fd52c20db71a7fccc45a36b3a2ae4d4c
+  rm d/four.txt
+  merkle-tree . # output back to  be343bb01fe00aeb8fef14a3e16b1c3d1dccbf86d7e41b4753e6ccb7dc3a57c3
+  echo "hidden-five" > a/b/one.txt
+  merkle-tree . # output changed  471fae0d074947e4955e9ac53e95b56e4bc08d263d89d82003fb58a0ffba66f5
+#+END_SRC
+It seems to work for this simple test case.
+** Using =merkle-tree= to check the output of =npm ci=
+/I've done all of the following using Node.js v8.11.3 and npm@6.1.0./
+
+In this test case I'll take the main repo of [[https://lernajs.io/][Lerna]][fn:js-repos]:
+#+BEGIN_SRC bash -n
+  cd /tmp/
+  git clone https://github.com/lerna/lerna.git
+  cd lerna/
+  git checkout 57ff865c0839df75dbe1974971d7310f235e1109
+  npm ci
+  merkle-tree node_modules/
+  rm -rf node_modules/
+  npm ci
+  merkle-tree node_modules/
+#+END_SRC
+Good job =npm ci= :)
+
+#6 and #9 take some time to run (21s in my machine), but this specific use case isn't performance sensitive.
+[fn:npm-install] The [[https://docs.npmjs.com/cli/install#description][documentation]] claims =npm install= is driven by the existing =package-lock.json=, but that' actually [[https://github.com/npm/npm/issues/17979#issuecomment-332701215][a little bit tricky]].
+[fn:js-repos] It was harder than I expected when I tried to find a big known repo that actually committed the =package-lock.json= file.